The 27-year-old is accused of murdering the South African model, whom he shot dead through a bathroom door at his home in Pretoria on Valentine's Day last year.
On day three of his testimony, Pistorius told the court that he "did not intend to kill" Steenkamp as he claims that he mistook her for an intruder.
As a graphic photo of Steenkamp's head injuries was shown to the court, prosecutor Gerrie Nel told Pistorius to "take responsibility for what you've done".
Nel appeared to order Pistorius to look at the image, but the double amputee refused and began crying. He said: "I've taken responsibility, but I will not look at a picture where I'm tormented by what I saw and felt that night. As I picked Reeva up, my fingers touched her head - I remember! I don't have to look at a picture, I was there!"
The athlete denies the charge of murder.